ABSTRACT In this study, we tested the impact of pretreatment with alcohol on subsequent alcohol drinking in outbred Sprague-Dawley and selectively bred alcohol-preferring (P) rats.
As a pretreatment, male Sprague-Dawley and P rats were given a passive oral administration of either alcohol (1.0 g/kg) or tap water. Then, they were given free choice of drinking alcohol (5% v/v) or water in their home cages, which was measured over 4 weeks.
Without alcohol pretreatment, there was no significant strain difference in alcohol preference; both strains preferred 5% (v/v) alcohol solution. The strain difference was only apparent in the groups given alcohol pretreatment. This arose from the fact that alcohol pretreatment significantly reduced alcohol preference in the Sprague-Dawley rats to a level well below 50%, while it did not alter drinking behavior in P rats. The same effects were seen with total alcohol consumption (g/kg/day). These effects persisted throughout the 4 weeks of the study.
The principal difference between the Sprague-Dawley and P rats was that the P rats did not show the normal aversion to alcohol after forced exposure to alcohol that the Sprague-Dawley rats showed. One of the potential contributors to high alcohol intake and preference in P rats may be lack of sensitivity to aversive effects of alcohol.

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Abnormal decision making under risk is associated with a number of psychiatric disorders. Here, we focus on binge drinkers (BD), characterized by repeated episodes of heavy alcohol intoxication. Previous studies suggest a decreased sensitivity to aversive conditioning in BD. Here, we asked whether BD might be characterized by enhanced risk seeking related to decreased sensitivity to the anticipation of negative outcomes.
Using an anticipatory risk-taking task (40 BD and 70 healthy volunteers) and an adapted version of this task for functional magnetic resonance imaging (21 BD and 21 healthy volunteers), we assessed sensitivity to reward and loss across risk probabilities.
In the behavioral task, BD showed a higher number of risky choices in high-risk losses. In the neuroimaging task, the high-risk attitude in the loss condition was associated with greater activity in dorsolateral prefrontal, lateral orbitofrontal, and superior parietal cortices in BD. Explicit exposure of BD to the probability and magnitude of loss, via introduction of feedback, resulted in a subsequent decrease in risky choices. This change in risk attitude in BD was associated with greater activity in inferior frontal gyrus, which also correlated with the percentage of decrease in risky choices after feedback presentation, suggesting a possible role for cognitive control toward risk-seeking attitudes.
Our findings suggest that a decrease in sensitivity to the anticipation of high-risk negative outcomes might underlie BD behavior. Presentation of explicit feedback of probability and loss in BD can potentially modify risk-taking attitudes, which have important public health implications and suggest possible therapeutic targets.

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The progressive predominance of rewarding effects of addictive drugs over their aversive properties likely contributes to the transition from drug use to drug dependence. By inhibiting the activity of DA neurons in the VTA, GABA projections from the rostromedial tegmental nucleus (RMTg) are well suited to shift the balance between drug-induced reward and aversion. Since cannabinoids suppress RMTg inputs to DA cells and CB1 receptors affect alcohol intake in rodents, we hypothesized that the endocannabinoid system, by modulating this pathway, might contribute to alcohol preference. Here we found that RMTg afferents onto VTA DA neurons express CB1 receptors and display a 2-arachidonoylglycerol (2-AG)-dependent form of short-term plasticity, that is, depolarization-induced suppres-sion of inhibition (DSI). Next, we compared rodents with innate opposite alcohol preference, the Sardinian alcohol-preferring (sP) and alcohol-nonpreferring (sNP) rats. We found that DA cells from alcohol-naive sP rats displayed a decreased probability of GABA release and a larger DSI. This difference was due to the rate of 2-AG degradation. In vivo, we found a reduced RMTg-induced inhibition of putative DA neurons in sP rats that negatively correlated with an increased firing. Finally, alcohol failed to enhance RMTg spontaneous activity and to prolong RMTg-induced silencing of putative DA neurons in sP rats. Our results indicate functional modifications of RMTg projections to DA neurons that might impact the reward/aversion balance of alcohol attributes, which may contribute to the innate preference observed in sP rats and to their elevated alcohol intake.

The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 09/2014; 34(38). DOI:10.1523/JNEUROSCI.1844-14.2014 · 6.75 Impact Factor

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1°C and relative humidity at 50 ± 10% and reversed light cycle(lights off: 0700–1900). The P and Sprague–Dawley ratsweighed an average of 373 ± 4.3 and 303 ± 4.3 g, respectively,at the beginning of the experiment. The treatment and care ofthe animals was carried out under an approved protocol of theAnimal Care and Use Committee of Duke University in an As-sociation for Assessment and Accreditation of LaboratoryAnimal Care-approved facility.Experimental protocolAt about 80 days of age, the rats were handled briefly for10 min/day for several days. Then, rats were given eitherone single dose of 1 g/kg alcohol (16% v/v) or an equal vol-ume of tap water by gavage once and only at the beginning ofthe experiment. To avoid possible taste aversion, all solutionswere directly delivered into the stomach and not into themouth. Fifteen minutes later, rats were placed in specializedpolycarbonate cages that were fitted with two 100-mL gradu-ated Richter drinking tubes for the recording of water andalcohol (5% v/v). The reason for choosing 5% alcohol ratherthan a higher concentration was that alcohol at this concentra-tion is more palatable for outbred strains of rats such asSprague–Dawley. Furthermore, with this concentration of al-cohol, there is less variability in drinking in outbred strains.Rats had a choice between water and alcohol for the remain-der of the study. Rats had continual access to water andalcohol for four consecutive weeks, and their water andalcohol intake levels were measured during the day at approxi-mately the same time. Procedures were similar to thoseroutinely used in our laboratory (Rezvani and Grady, 1994;Rezvani et al., 1995; Overstreet et al., 1996; Rezvani et al.,1997, 1999, 2000, 2007, 2009).Preparation of alcohol solutionsA solution of 5% (v/v) alcohol was prepared twice weeklyfrom a solution of 100% ethanol mixed with tap water.Statistical analysis of dataAlcohol intake was calculated as grams per kilogram from avolume of 5% (v/v) alcohol consumed. Alcohol preferencewas calculated as a percentage of alcohol consumed over totalfluid intake (alcohol + water). Means were calculated and sub-jected to ANOVAwith strain and pre-testing alcohol treatmentas between-subjects factors and weekly averages of percentalcohol vs water preference and grams per kilogram per dayof alcohol intake. Significant interaction effects were followedup by tests of the simple main effects of each strain at eachpre-testing alcohol treatment condition to determine which in-dividual strain and treatment groups differed from each other.A P-value of 0.05 (two-tailed) was used as the threshold forsignificance.RESULTSFor amount of alcohol consumed (g/kg/day), there was not asignificant main effect of strain (P = 0.098). However, therewas clearly a significant interaction of strain × alcohol pretreat-ment (F(1,27) = 7.27, P < 0.025). As displayed in Fig. 1A(mean alcohol consumption over 4 weeks), the tests of the sim-ple main effects showed significantly (P < 0.005) greateralcohol consumption in P rats than Sprague–Dawley rats whenthere was alcohol pretreatment, but not when the pretreatmentwas only water. This did not result from the induction of alco-hol drinking by alcohol pretreatment in P rats. They did notsignificantly change their consumption with alcohol pretreat-ment. Rather, it was the Sprague–Dawley rats that showed asignificant (P < 0.005) decrease in alcohol consumption afteralcohol pretreatment by nearly 50%. Fig. 2A shows the de-tailed week-by-week levels of alcohol consumption. Therewas a significant main effect of week (F(3,81) = 13.30, P <0.0005) with an overall increase in alcohol consumption overweeks. There was no significant interaction of weeks with ei-ther strain or alcohol pretreatment. The lower amount ofalcohol consumption in Sprague–Dawley rats with pre-expo-sure vs Sprague–Dawley rats without alcohol pre-exposure aswell as relative to P rats pre-exposed to alcohol was maintainedthroughout the 4-week study. Sprague–Dawley and P ratswithout alcohol pre-exposure did not differ in alcohol consum-mation at any point in the 4-week study.The percent alcohol preference measure showed similar re-sults. With percent preference, there was a significant maineffect of strain (F(1,27) = 14.80, P < 0.001) with the P ratshaving a higher preference for alcohol than the Sprague–Dawley rats (81.1 ± 3.6% vs 52.0 ± 7.3%); however, this re-sulted completely from the lower alcohol preference in theSprague–Dawley rats given alcohol pretreatment (Fig. 1B).There was no significant difference in the preference betweenthe strains when no alcohol pretreatment was given. As withAB0.00.51.01.52.02.53.03.54.0Alcoholg/kg/daySprague-Dawley P-RatsEffect of Alcohol Pretreatment on Alcohol Consumption in Sprague-Dawley and P-rats: Average over Four WeeksAlcoholVehiclePretreatmentp<0.005p<0.0050102030405060708090100PercentAlcoholPreferenceSprague-Dawley P-RatsEffect of Alcohol Pretreatment on Alcohol Preference in Sprague-Dawley and P-rats: Average over Four WeeksAlcoholVehiclePretreatmentp<0.005p<0.0005Fig. 1. (A) Effects of an oral dose (1 g/kg) of alcohol administration on sub-sequent alcohol intake (g/kg/day) in alcohol-preferring P and Sprague–Dawley rats. Data represent the means ± SEM of 4 weeks. N = 8 for eachgroup of Sprague–Dawley rats, 9 for vehicle-treated P rats and 6 for alcohol-treated P rats. (B) Effects of an oral dose (1 g/kg) of alcohol administration onsubsequent alcohol preference in alcohol-preferring P and Sprague–Dawleyrats.Data represent the means ± SEM of 4 weeks.N = 8 for each group of Spra-gue–Dawley rats, 9 for vehicle-treated P rats and 6 for alcohol-treated P rats.Rezvani et al.220

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alcohol consumption, there was a significant strain × alcoholpretreatment interaction (F(1,27) = 7.41, P < 0.025). Follow-up tests of the simple main effects showed that alcoholpretreatment significantly (P < 0.005) reduced alcoholpreference in the Sprague–Dawley rats while the P rats didnot show a change. There was a significantly (P < 0.0005)greater alcohol preference in the P rats pretreated with alcoholvs pretreated Sprague–Dawley rats. Sprague–Dawley ratsshowed aversion to alcohol with only 36.0% preference forthe alcohol-containing bottle. This was well below the 50%chance level and the 68.1% level shown by Sprague–Dawleyrats not given alcohol pretreatment. This is the same pattern ofeffects as shown with the grams per kilogram per day alcoholconsumptionmeasure.Fig.2Bshowstheweek-by-weekbreak-down in alcohol preference by the groups. As with theconsumption, the preference data showed a significant maineffect of weeks (F(3,81) = 14.03, P < 0.0005) with overallincrease in percent preference over weeks. There were nosignificant interactions of weeks with either strain or alcoholpretreatment.AsshowninFig.2A,theeffectofasinglealcoholpretreatment was clearly seen during the fourth week of thestudy.DISCUSSIONThe results of this study demonstrate that selectively bred al-cohol-preferring P rats, compared with Sprague–Dawley rats,are less sensitive to the aversive effects of alcohol. Sprague–Dawley rats showed a long-lasting decrease in alcohol con-sumption and preference for 4 weeks after a single alcoholpretreatment. On the other hand, the P rats given the same al-cohol pretreatment showed no such effect. Without alcoholpretreatment, there were no discernible differences betweenSprague–Dawley and P rats in either the amount of alcoholconsumed and the percent alcohol preference. The lack of dif-ference in alcohol preference between Sprague–Dawley and Prats before being treated with alcohol is likely contributed tothe palatability of 5% (v/v) alcohol. It is likely that at higherconcentrations of alcohol, the P rats will drink significantlymore alcohol than Sprague–Dawley rats. The increased alco-hol consumption seen in P rats seems to be entirely due to alack of the normal aversion to initial alcohol treatment ratherthan increased preference. It has previously been shown thatthe P rats self-administer significant quantities of alcohol in-tragastrically, indicating that post-absorptive effects ofalcohol, rather than its taste or smell, are reinforcing for theP rats (Waller et al., 1983a). It has also been demonstrated thatP rats find the post-ingestional effects of high dose of alcoholless aversive and low dose of alcohol more rewarding thantheir control counterpart, the NP rats (Froehlich et al.,1988). The possible effects of taste in the current experimentshould be ruled out because alcohol solution was delivereddirectly into the stomach and not into the mouth. Genetic dif-ferences in sensitization and tolerance development to alcoholbetween the P and NP rats have also been reported. Kurtz andcolleagues (1996) studied the initial sensitivity to alcohol andthe development of tolerance comparing the P with the NPrats. They demonstrated that P rats were less sensitive to thebehaviorally impairing effects of alcohol than were NP rats, asevidenced by longer latency to lose righting reflex and ashorter time to recover following an acute dose of alcohol.It has also been shown that within-session tolerance to alcoholis developed in P rats (Waller et al., 1983b). Thus, it can bespeculated that the combination of lack or less sensitivity toalcohol, less aversion to alcohol and development of acute tol-erance to alcohol may serve to increase alcohol intake in Prats. As mentioned in the Introduction, in the conditioned tasteaversion (CTA) paradigm (Froehlich et al., 1988) and in theconditioned place preference (CPP) paradigm (Stewart et al.,1996), both P and NP rats showed aversion to alcohol. How-ever, the magnitude of aversion to alcohol was significantlyless in P rats compared with NP rats. In one study, no differ-ence was found between P and NP rats using the CPPparadigm (Schechter, 1992). Our results should not be directlycompared with CTA and CPP results because measuringdrinking alcohol is the most appropriate test for testing aver-sion to alcohol in rats that have been selectively bred to drinkalcohol.Thefactthat onesingleintragastricadministration ofalcoholimpaired acquisition of alcohol drinking in Sprague–Dawleyrats but not in P rats suggests that this selectively bred linemight have less aversion to alcohol than the outbred Spra-gue–Dawley line. One can speculate that the diminishedaversion to alcohol may partly explain the high level of drink-ing in selectively bred P rats.Interestingly, similar findings have been reported in humansregarding the importance of diminished aversive effects of al-cohol in alcoholics. A lower level of response, i.e. lowersensitivity to subjective and intoxicating effects of alcohol,AB012345Alcoholg/kg/dayWeekEffect of Alcohol Pretreatment on Alcohol Consumption in Sprague-Dawley and P-rats: Weekly IntakeP-rats/AlcoholP-rats/No AlcoholSprague-Dawley/AlcoholSprague-Dawley/No AlcoholStrain and Pretreatment0102030405060708090100PercentAlcoholPreference12Week341234Effect of Alcohol Pretreatment on Alcohol Preference in Sprague-Dawley and P-rats: Weekly ChoiceP-rats/AlcoholP-rats/ No AlcoholSprague-Dawley/AlcoholSprague-Dawley/No AlcoholStrain and PretreatmentFig. 2. (A) Effects of one single oral dose (1 g/kg) of alcohol administrationon subsequent alcohol intake (g/kg/day) in alcohol-preferring P and Sprague–Dawleyrats.Datarepresentthemeans±SEMofweeklyintakefor4weeks.N=8 for each group of Sprague–Dawley rats, 9 for vehicle-treated P rats and 6 foralcohol-treated P rats. (B) Effects of one single oral dose (1 g/kg) of alcoholadministration on subsequent preference for alcohol in alcohol-preferring Pand Sprague–Dawley rats. Data represent the means ± SEM of weekly intakefor4weeks.N=8foreachgroupofSprague–Dawleyrats,9forvehicle-treatedP rats and 6 for alcohol-treated P rats.Lack of Aversion to Alcohol in P Rats221